Design Methodology for Strengthening of Continuous-Span Composite Bridges

Abstract

Increases in legal-load limits as well as lack of maintenance has rendered a large number of bridges in the United States deficient and in need of rehabilitation or strengthening. Many of these bridges are classified as deficient because their load-carrying capacity is inadequate for today's traffic. This paper deals with two methods of strengthening understrength bridges: posttensioning of the positive moment regions of bridge stringers and the addition of superimposed trusses to the stringers at the piers. These strengthening methods have been verified experimentally and analytically through a number of Iowa Department of Transportation (Iowa DOT) research projects. In most continuous-span bridges, the desired stress reduction in the stringers can be achieved by posttensioning only the positive moment regions. However, in certain situations, superimposed truss systems are needed at the piers to obtain the desired stress reduction in the negative moment regions. This paper presents the development of a design methodology for use by practicing engineers in designing a strengthening system (posttensioning in positive moment regions and/or superimposed trusses in negative moment regions) for continuous-span composite bridges.